Hot-melt adhesives are used extensively for case and carton sealing on automated packaging machinery, as well as other assembly line applications. For example, FIGS. 1 and 2 illustrate hot-melt adhesive dispensers 10 and 12 in use in an automatic packaging assembly line. The dispensers 10 and 12 are described in detail in U.S. Pat. No. 4,659,016 to Faulkner, III, assigned to the assignee of the present application. As a carton 14 moves along rollers, not shown, hot-melt adhesive is dispensed from nozzles 16 to the outside surfaces of top minor flaps 18 of the carton and to inside surfaces of the bottom major flaps 20. The top-apply dispenser 10 has an inverted T-shaped configuration with the nozzles 16 placed on the front side of a multi-orifice nozzle manifold 22. The bottom-apply dispenser 12 has a Y-shaped configuration with the nozzles 16 supported on a split multi-orifice nozzle manifold 24. Melted adhesive from pressurizing tanks, not shown, is channeled to solenoid valves 26 via hoses 28. Fastening hardware 30 secures a hose 28 to the associated solenoid valve 26. Actuation of the solenoid valve 26 regulates fluid communication between the hose 28 and a plurality of nozzles 16 of the associated nozzle manifold 22 and 24. Thus, the adhesive dispensers 10 and 12 are single-valve dispensers.
Adhesive flow from the solenoid valve 26 is through a heater block 32 having thermal units to maintain the adhesive in a melted state. Brackets 34 are mounted to the heater blocks 32 by bolts 36, fixing the dispensers 10 and 12 in position.
The nozzle manifold 22 is comprised of a center inlet portion 38 and a pair of longitudinal dispenser bars 40, only one of which can be seen in FIGS. 1 and 2. After progressing through the solenoid valve 26 and the heater block 32, adhesive enters a coupling assembly having a pair of swivel nuts 42 and 44 for passage to the inlet portion 38 of the nozzle manifold 22. The coupling assembly places the nozzle manifold in a direct hot-melt material dispensing line with the heater block. As will be explained more fully below, the coupling of the heater block to the nozzle manifold is an important feature of a dispenser 10 and 12. Briefly, this importance lies in the coupling's effect on nozzle drool between separate adhesive applications and in the ability to compensate for dimensional differences where less than exact manufacturing tolerances are dictated. The coupling assembly which includes swivel nuts 42 and 44 provides an inelastic coupling, and the swivel nuts allow for dimensional tolerances of the interconnected heater block 32 and nozzle manifold 22.
An advantage of the above-described dispensers 10 and 12 is that a single solenoid valve 26 controls adhesive flow to all of the nozzles 16 of a nozzle manifold 22 and 24. Dispensers having a separate valve for each separate nozzle tend to have varying flow rates across the different nozzles. Another advantage is a result of the relationship of the solenoid valve 26, the heater block 32 and the nozzle manifold 22. Where a heater is downstream of a valving point, nozzle drool is a concern. Adhesive which is locked within a heating area may experience a rise in temperature. The coefficient of thermal expansion of the adhesive determines how much drooling will occur if heating of a nozzle manifold causes expansion of adhesive within the manifold. Such expansion forces adhesive from nozzles.
A characteristic of dispensers 10 and 12, however, involves the necessity of the coupling assembly that includes swivel nuts 42 and 44. While thermal expansion in the nozzle manifold is undesirable because nozzle drool will result, it is desirable to minimize any cooling during the passage of hot-melt adhesive through the nozzle manifold, especially during periods between applications when the adhesive is held in the manifold for an extended time. The dispensers 10 and 12 include heat transfer blocks 46 which provide a heat flow path that is separate from the adhesive flow path from the heater block 32 to the associated nozzle manifold 22 and 24. The heat transfer block accomplishes its intended purpose, but is less thermally efficient than would be a direct coupling of the heater block 32 to the nozzle manifold. Such direct coupling is difficult, however, without increasing the tendency of the nozzles 16 to drool between applications. Characteristics of a drool-retardant coupling must include a leak-resistant seal, an inelastic fitting, and an absence of air pockets. Inelasticity inhibits drool-causing expansion and contraction of the coupling as the solenoid valve 26 is activated and deactivated. Air is an expandable gas and air pockets result in a push of the glue at the end of each adhesive application. The coupling assembly of FIGS. 1 and 2 possesses the desired characteristics but at a sacrifice of efficiency of heat transfer to the nozzle manifold.
It is an object of the present invention to provide a hot-melt adhesive dispenser in which a nozzle manifold is downstream of a heating member, with a coupling that enhances thermal efficiency while maintaining the desired characteristics of inelasticity, leak-resistivity, and an absence of air pockets.